Mercury relay



March 27, 1962 vl. L. MITCHELL MERCURY RELAY Filed NOV. 17. 1959 INV EN TOR. /i'w/vf,` L. M/TCHELL BY ATTOR/VBVYS 3,027,437 Patented Mar. 2?, 1962 tice 3,027,437 MERCURY RELAY Irving L. Mitchell, Rockville Centre, N.Y., assignor to Ebert Electronics Corporation, Queens Village, NX., a corporation of New York Filed Nov. 17, 1959, Ser. No. 853,647 5 Claims. (Cl. Zim-112) The present invention relates generally to mercury relays, and more particularly to mercury relays of the mercury displacer type comprising an envelope having two electrodes adapted to be bridged by the mercury, the electrodes being relatively insulated while the mercury level is low during a first location of the displacer with respect to the mercury, the electrodes being bridged by the mercury when the level of the mercury is high during an alternative location of the displacer, and more particularly to a novel time delay element in mercury relays of the displacer type, having provision for extremely accurate and stable adjustment of the delay time between actuation of Ithe displacer and bridging of the electrodes, and to novel displacers including metering elements arranged to provide rapid electrode bridging and delayed electrode debridging by the mercury of the relay.

It has long been known, in mercury switches of the displacer type, to provide for delayed actuation of the displacer by causing the latter to trap gas in a chamber formed by the displacer and the surface of the mercury, permitting the gas to leak slowly from the chamber through a porous plug, or through a plug of tapered character which less than completely lls a correspondingly tapered aperture in the displacer.k Such systems have not been found to be stable in respect to the times of delay introduced thereby, because of difficulty in reproducing the porous plugs, and because the porous plugs change their characteristics with aging, and in the case of the tapered plug type of gas metering device, because the lit of the taper within its mating aperture is subject to change by vibration and shock and further because of the difficulty of accurately and precisely adjusting the tapered plug within its mating aperture, on a mass production basis.

It is a feature of the present invention to provide a novel mercury relay of the displacer type, in which the displacer forms a chamber enclosing one of the electrodes of the relay, the other electrode being permanently immersed in the mercury pool of the relay, and in which a gas escape metering element is included in the Wall of the displacer, the metering device being constituted of an extended orilice formed by threads of a threaded aperture and a threaded set screw or plug, which threadedly engages the aperture to a selective extent by threading the set screw to a greater or lesser eXtent'into the threaded aperture. The length of the metering orifice may beV adjusted with extreme accuracy and once adjusted may be made permanent by slightly upsetting the set screw, so that ity cani not be further rotated in response to shock or vibration. The importance of theinvention resides in the precision with which the metering opening may be adjusted, and further in the fact that once adjusted it does not vary over the entire life of the relay of which it forms a part.

As a further feature of the invention the displacer is formed of a ceramic liner on which is superposed a cylindrical magnetic plunger, and above which is located an inverted dome fabricated of any suitable material, a slight gap exis-ting between the liner and the dome, at their junction, to permit rapid escape of gas. Accordingly, when the coil of the relay is energized, forcing the plunger downwardly into the mercury pool, the ceramic element enters the pool rapidly, since the gap between the ceramic liner and the dome permits the rapid escape of gas. The level of the mercury pool is thus raised sufficient-ly to effect bridging of the electrodes of the relay prior to the time that the dome enters the mercury pool. Once the dome has entered the mercury pool escape of gas can occur only through the metering orifice at the set screw, there being no gap between the dome and the liner, and suc-h escape is slow, so that the plunger terminates its motion very slowly. Nevertheless, the electrodes are bridged rapidly in response to energization of the coil of the relay. On deenergizing the coil the plunger tends to rise due to the buoyancy of the depressor structure within the mercury pool. However, this rise is delayed ab initio by the fact that gas must traverse the metering orifice from externally of the dome to the chamber formed internally thereof. Accordingly, the rise of the plunger is slow in its initial motion, but when the plunger has risen to the point for which the upper edge of the liner is coincident approximately with the surface of the mercury pool, gas

escapes from the interior of the chamber rapidly and the last part of the motion of the plunger is rapid. It is during this latter part of the motion of the plunger that the bridge between the electrodes formed by the mercury of the pool is broken.

Accordingly, in the opera-tion of the presently described embodiment of the present relay, a circuit is made rapidly but is broken slowly, i.e., with a time delay, and this time delay is accurately metered by a novel metering orifice. Nevertheless, the relay as described may be readily modified, to provide for delayed make and delayed break, by modifying the relative dimensions of its parts and the quantity of mercury in the mercury pool so as to cause both make and break to occur only after the rim of the dome has become submerged, and the relative times of make and break may be adjusted in this manner, i.e., these times may be equal or unequal.

It is, accordingly, a broad object of the present invention to provide a novel mercury relay of the depressor type in which is provided a metering orifice for controlling escape of gas from a chamber formed by the depressor and the surface of the mercury pool, the metering orifice being formed by a set screw, which threadedly engages the threaded aperture to form an orice of adjustable length.

It is a further object of the invention to provide a novel and accurately timed mercury pool relay of the displacer type, which operates rapidly to make a circuit in response to energization of a coil surrounding the switch structure of the relay but which operates to break the circuit only after a predetermined time delay.

It is a further and broader object of the invention to provide a novel mercury relay of the displacer type, which may be arranged to perform predetermined switching operations only after predetermined time delays.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawing, wherein:

FIGURE 1 of the drawing is a view in front elevation of a mercury relay according to the present invention, with displacer raised;

FIGURE 2 is a view of the relay of FIGURE l with displacer depressed; and

FIGURE 3 is a View of a modified form of displacer.

Referring now more specifically to FIGURES 1 and 2 of the accompanying drawings, the reference numeral 10 denotes a relay-operating coil, surrounding an enclosed glass envelope 11, which contains a pool of mercury 12. The glass envelope 11 is an approximately cylindrical tube, sealed at both ends, and is arranged with its axis vertical, so that the mercury pool 12 collects at the bottom ofthe glass tube 11. Extending through a glass seal 13, formed by pinching together the walls of the glass tube 11 at its bottom end, is a bare electrode 14, and adjacent thereto and extending through the seal 13 is an insulated electrode 15. The insulated electrode 15 extends through the mercury pool 12, and into a ceramic cup 16, being bare only within the cup 16, so as to make electrical contact with any mercury contained within the cup 16. The normal level of the mercury pool 12 is below the level of the upper rim of the cup 16, the normal level being that for which a displacer 17 is in its elevated position, floating freely in the pool 12. The displacer 17 is in its elevated position so long as the coil 10' is noty energized, and includes an inverted dome 18 having in its peak a threaded aperture 19 within which is threadedly engaged a set-screwor threaded plug 20. The dome 18 is secured to a magnetic sleeve 21 which` is cylindrical in shape and which includes a plurality of projections 22, adjacent its upper edge and adjacent its lower edge, the projections 22 serving as guide elements for the dome 18 as the latter moves vertically upwardly and downwardly in the glass tube 11 in responsey to de-energization and energization respectively of the coil 10. Secured vinternally'of the sleeve 21 and concentric therewith is a hollow cylindrical ceramic liner 23, comprising an element of the able time delay, but upon Ide-energizing the coil 10 the circuit is broken only after a time delay equal to the time required for the dome 18 to rise to a point at which the gap 25 is no longer covered by the mercury pool 12.

It follows that the delay time Vfor opening of the switch Vof the relay of the'present invention may be adjusted on ingly the total time required for -a given volume of thek i gas to escape lcngthens. v i

The actual process .of making and breaking the circuit formed by the electrodes 14 and 15 always occurs rapidly, which reduces the possibility of arcing. Y

It will be evident that the relay as described may readily be modified structurally to provide for delayed make and delayed break, and this may most readily be done by decreasing the quantity of mercury in the mercury pool, if other dimensional features of the relay are to remain unmodified. v Y

VIn FIGURE 3 of the accompanying drawings is illustrated a modification of the displacer 17 system of FIG- URES 1 and 2, in which is utilized a ceramicliner 30,

displacer 17, and which extends downwardly from the dome 18, and which at its upper rim 24 is slightly spaced from the lower rim of the dome 18. The space between the dome 18 and the liner 23, identified by the reference numeral 25, provides a relatively large escape path for thegas which normally fills the interior of the tube 11. The displacer. 17, and particularly the dome 18 which forms its uppermost portion, forms ya hollowrchamber 26 which is generally co-extensive with the interior of the ceramic liner 23. The ceramic liner 23 and the plunger 17a, being both secured rigidly to the sleeve 21, move together as a unit. The ceramic liner 23 normally iioats in the mercury pool, with its upper rim 24 exposed, since the total weight of the ceramic liner 23 and or" its dome 18 is low. Upon energization of the coil 1i), the displacer 17 is drawn downwardly into the mercury pool 12 and this action is initially relatively rapid, since during this action the gas trapped within the chamber 26 formed by the dome 18 and the plunger 17a can escape through the relatively large opening 2S at a rapid rate. As the ceramic liner moves downwardly the level of themercury pool 12 is raised, eventually attaining the level above that of the upper rim of the cup 16, at which point a circuit is completed between the electrodes 14 and 15, by bridging of the mercury exteriorly of the cup 16 with the mercury interiorly of the cup 16. At this point the gap 25 has not yet been covered by the mercury pool, and gas can escape rapidly from the chamber 26, via the gap 25, so that the entire process of completing a circuit in response to energization of the coil 10 is accomplished rapidly, i.e., without appreciable time delay.

Upon breaking the circuit to the coil ,iti the depressor comprising the displacer 17 and the ceramic liner 23 tends to rise, due to its own buoyancy, but the gap 25 is at this point covered by the mercury pool `and accordingly the displacer cannot rise except insofar as gas escapes through the metering orifice deiinedby the adjustable set screw 2t) andthe threaded opening 19 with which it is threadedly engaged. This oriiice is extremely small, so that the gas escapes therethrough very slowly, and accordingly the displacer rises very slowly until the gap 25 rises above the level of the mercury` pool 12. At this point the circuit between the electrodes has not yet been broken. When the gap '25 attains the level of the mercury pool 12, the gas trapped within the dome 18 is rapidly released, the dome rapidly risesand the bridge between the electrodes is broken during this rapid rise. Accordingly, on Venergizing the coil 10 the circuit between'the electrodes 14tand 15 is made without apprecihaving a magnetic sleeve 21 secured thereabout, and forming a dome having a'set screw 2t) directly therein.V The liner 30 is provided with a horizontal slot 31, or several of i these if desired, and the level of the slot 31 determines in part the 'operating characteristics of any relay including the displacer.

While l have described and illustrated one specific ernbodiment of my invention, it will be Clear that vari-ations of the details of construction which are specifically illustrated and dened may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims. Y

What I claim is: Y 1. A mercury relay of the displacer type, comprisim a pool of mercury, a container for said pool of mercury,

a first electrode insulated from said pool of mercury and having-a conductive element located above the normal level of said pool of mercury for contact with said mercury only on predetermined rise of sai-d normal level, a quantity 4of gas within said container, and a depressoroating in said pool of mercury, said depressor including a gas trapping inverted device having a rim normally subsistingy above said normal level, a metering orice for said gas located in said dome, said displacer including magnetic material and being gas tight except for said metering oriiice, said rim of said dome, said predetermined level of said pool of mercury, and the location of said second electrode, each with respect to the others, being so located threaded plug threadedly engaging said aperture, said orifice extending along the threads of said orifice, whereby the length of said orifice is adjustable by rotation of` said threaded plug. r

4. ln a mercury switch, a pool. `of mercury, a mass of gas located above said poolV of mercury, a pair of contacts, means for varying the level of the surface of said pool of mercury between two predetermined levels, said means being a mercury displacer oating in said pool of mercury, said contacts being so located as to be bridged by said mercury at `one of said predetermined -levels and unbridged at the other of said predetermined levels, means for actuating said mercury displacer into and out of said pool of mercury so as to vary said level of said sur-face selectively between said two predetermined levels, and means for delaying actuation of said displacer comprising a gas metering vdev-ice secured to said displacer, said gas metering device comprising a dome fabricated of magnetic material, said dome defining a gas trapping chamber and having its concave side facing said surface, and having a rim which subsists at least approximately parallel to said surface, said dome being provided with a ceramic liner secured to said dome and extending thereunder and into said pool of mercury, said ceramic liner constituting a oater for said dome, and said ceramic liner including an upper rim, a substantial air gap between said rim of said dome and said upper rim of said liner, the buoyancy of said liner and said dome in said pool of mercury being adequate to sustain said dome normally outside said pool of mercury, said air gap being positioned to be submerged in said pool of mercury only in the depressed state of said displacer.

5. The combinationI according to claim 4 wherein said gas metering device includes a threaded aperture in said dome, and a threaded plug threadedly engaging said aperture;

Putt July 24, 1934 Larson July 18, 1939 

